Just as the situation turns to their advantage, Brexit fellow-travellers are turning their fire on each other. It is the most baffling spectacle, born out of the weirdo psychological instincts of tribal political campaigns.

Over the weekend, there was another volley of attacks from People's Vote campaigners towards Norway supporters. The normally brilliant David Lammy was in the Guardian saying that Norway would "betray" Leave and Remain voters. Bridget Phillipson was writing in the Independent that Norway was "a fantasy". Last month, Jo Johnson argued that Norway was a "non-starter".

There's plenty of return fire in the other direction. Norway supporter Nicky Morgan has promised not to support a second referendum. George Trefgarne, writer of Norway then Canada, spends half his time on Twitter attacking anyone trying to secure a change in policy other than the one he has authored - whether it's Tony Blair or Dominic Grieve or the People's Vote.

On a purely strategic level, this is self-harming and short-sighted. If the People's Vote campaign fails, which is a perfectly realistic scenario, it needs Norway as the Plan B. Britain will be outside the EU, with a future relationship document which can be amended. The most important battle in politics will be to soften it so that it allows for Norway. By attacking it now, those People's Vote figures essentially rule themselves out that fight. Anything they say to support Norway in 2020 will be instantly met by a quote from their attacks on it now.

Worse, the attacks bolster the Brexit case. When People's Vote types complain that Norway offers no change to free movement, for instance, they are undermining their own demands for full EU membership - because that does not change free movement either. They're legitimising questions to which they themselves have no answer.

And all of this anyway has no function. To get Norway you need to pass a withdrawal agreement through the Commons. And that withdrawal agreement will have a backstop in it. The ERG and DUP will never accept that, so the only way it could pass would be with Labour support, which is not forthcoming. There is no immediate Norway threat to the People's Vote. As a mere question of priorities, the attacks on it are downright bizarre.

Norway must survive as a sub-optimal outcome in case of failure. But People's Vote seem intent, either by central decision-making or simply because lots of disparate voices think it sensible, to attack it.

Norway supporters make the same mistake. Fine, they don't like the idea of a second referendum. Very few people are entirely enamoured with the idea. But look at the options in play. May's deal is dead. Any deal looks unlikely. That leaves the People's Vote on one hand and no-deal on the other. You may not like either option, but there is no comparison in terms of severity.

No-deal will pulverise this country economically, while pursuing an extreme plan with no mandate, amid hard-right rhetoric about immigration and xenophobia. It is arguably the most extreme proposition ever made in mainstream British political debate. And it is real. It must be stopped at all costs. There is no greater patriotic priority.

That means that there should be no attempts to undermine campaigns opposing it. They are allies, not competitors. And you should never attack so comprehensively that you're unable to later offer support if your own preferred model fails.

We truly are in the era of purity politics. Political campaigns, on both sides of the divide, seem increasingly unable to understand the language of compromise, cooperation and tolerable sub-optimal outcomes. In politics, you can pursue your ideal goal while also maintaining the possibilities for a maximised negative outcome. You can simultaneously fight for what you want while limiting the damage of what you don't. Any married couple understands this strategy. It is remarkable that seasoned political campaigners are unable to do so.

This is more than just a tactical instruction. It is the basis upon which a healthy democratic society operates. A culture in which people cooperate with other political groups for mutual advantage is one which understands basic norms of civilised disagreement.

The winner-takes-all, zero-sum assessment of politics, in which the only true allies are your fellow tribal members, is just base Trumpism, whether it comes in reactionary, moderate or progressive variants. It is a political attitude which undermines the values of the society it is trying to salvage.

Norway and People's Vote have more in common than divides them. It's about time they started acting like it.

Just when you think there is no further your expectations can fall, they find a way to surpass them. It's hard to imagine any two political figures behaving with less conviction or decency than Theresa May and Jeremy Corbyn this week. We must have truly done something terrible in a previous life to deserve this.

At any other time, you'd presume that we'd reached some sort of nadir, a basement dungeon of political decency, beyond which it was impossible to fall. But this is Brexit, so they will invariably exceed themselves next week.

May's attempt to 'reach out' in the wake of her historic defeat this week was as self-interested and false as it was possible to imagine. She refused to make any changes to her proposals at all. She was not willing to change her policy in the slightest.

Instead, she appeared only interested in using the talks for short-term political advantage. A Downing Street statement was arranged for just hours after her invite, seemingly with the sole intention of pointing out to people that Corbyn had not attended yet. Those politicians who did attend talks - The Green's Caroline Lucas, the Lib Dem's Vince Cable, the SNP's Ian Blackford, and others - said there was nothing new on the table and that they wouldn't bother attending again unless something changed.

Corbyn saw how badly the prime minister was failing to live up to the moment and tried to match it. There is a kind of solidarity of irresponsibility between the two. Or perhaps it is a competition.
The Labour leader demanded that the prime minister "rule out" no-deal as a precondition for talks.

This is a standard tactic of parties who do not want to engage. It's equivalent to when governments demand a terrorist group renounces violence before entering into talks with it. It treats the ultimate aim as a precondition of holding negotiations to achieve it.

These talks are a way to stop May from allowing no-deal. They are a chance for opposition parties to get her to pull on the brakes. But there is no point simply demanding that as a precondition of holding the talks at all. That is a party political game.

Even if May said she ruled out no-deal, it would be a meaningless promise. No-deal happens automatically on March 29th as a result of the Article 50 notification. It is the default outcome. To stop it, we need a parliamentary majority for something. That could be a motion demanding the government petition for an extension to Article 50. Or it could be legislation to hold a People's Vote, with an attached extension. Or perhaps a new mandate for talks on customs union and single market membership, again with an attached extension provision.

Even if we were simply to revoke Article 50, we would still need a parliamentary majority. The European Court of Justice ruling allowing the UK to unilaterally cancel Brexit stated that it had to do that in accordance with its constitutional arrangements. And the Gina Miller case, back in the halcyon days of 2017, showed that governments cannot use the royal prerogative to overrule a decision which has been taken by parliament. In this case, parliament voted to trigger Article 50. So either by a motion or a piece of legislation - there is a lively legal debate on exactly which - there needs to be a majority even to cancel Article 50.

Of course, none of this really matters. Whether Corbyn holds talks with May or not is immaterial. She refused to give the talks meaning, because she ruled out making any changes to her policy on the basis of them. And he ruled out taking part in the talks by saying he would not participate unless she made the changes in advance. This has been an utter waste of our time.

They are the most inadequate, self-interested, unimaginative, unprincipled, irresponsible party leaders in living history. There is no thesaurus in the world which could contain all the descriptions of their failures. In a moment which requires towering political figures, we're lumped with them: a prime minister with the intellectual status of a pebble and an opposition leader with the cerebral qualities of crumbled paper.

It cannot possibly be any clearer that these two figures have failed the country and are incapable of living up to the historic moment they find themselves in.

It is now up to MPs to take the lead. There are proposals floating around Westminster to give parliamentarians control over the Commons timetable. This could be attached as an amendment to May's motion on what she plans to do next. It is imperative that this now passes. There are no other routes of preventing disaster. Parliament must formally take control.

This moment has shown us what terrible political leaders we have ended up with. When things are quieter, we can ask ourselves some searching questions about how that came to pass. For now, there is just one cheerful thought. Their inadequacy might force a constitutional change which gives parliament lasting powers over the executive. That would be the closest thing we ever find to a Brexit dividend.

Yesterday was Theresa May's turn. All her various failings were laid bare: her short-sighted red lines, her self-harming cultivation of ERG Brexit myths, her presentational inadequacy, her lack of political empathy, and her utter strategic incompetence. It finally all came together in a historic humbling - the worst defeat of a prime minister in parliamentary history.

Today it's Corbyn's turn. His attempt at a no-confidence motion against the government, the one he had tried to avoid, was defeated by 325 votes to 306. As expected, the DUP stepped in to protect the prime minister. The Labour leader is now at exactly the point he wanted to avoid: the moment when he has to come up with a Brexit policy which does not involve him pretending that a general election would somehow magically fix everything.

Some senior Labour figures now insist that their policy is simply to keep firing off these confidence motions, pointlessly, only for the DUP to keep deflecting them away. That is not a policy. That is a continuation of a holding pattern, which they intend to pursue while the country falls apart.

The time for Corbyn's 'constructive ambiguity' over Brexit is over. The spotlight is now on him. There is no place left to hide.

For the last two and a half years, the leader of the opposition has been an absence. Brexit is the only political debate taking place in this country and he showed no interest in discussing it. His own Brexit proposals, apart from customs union membership, are vague to the point of meaningless.

His supporters will say that there are other things wrong with this country. And they're right. Austerity has been a moral outrage and an economically illiterate failure. The NHS and housing have been in crisis so long we've stopped noticing it. Our criminal justice system is useless. We've hollowed out the economy so that it is split between insecure low income jobs and highly paid professional ones, with few ways of going from one to the other.

But there's no point pretending you can just ignore Brexit. You can't treat it like any other political issue. It dominates everything. We're discussing the entire trading structure of the country. There's no money for the NHS if we get this wrong. There's no money for housing. And on a deeper social level, there is no chance for an open, compassionate, left-wing country when you hand the keys to a bunch of right-wing xenophobic fantasists.

We'll never know how much we lost because of Corbyn's absence. We'll never know if a forensic opposition leader, who scrutinised the government and offered a credible alternative strategy, could have helped shift the Brexit policy as it was formulated. That opportunity is now lost. What we do know is that he can play a decisive role in what happens next.

The government, as a functional operation, is dead. The DUP have put it on life support, but it sits in Downing Street as a purely symbolic entity, not one which is capable of actually doing things. It has no ideas. It has no plan. It has no mandate. It was denied its majority at the election and its Brexit deal has been annihilated.

Parliament has no majority for any option, be it no-deal, an alternate deal, or a People's Vote. The various groupings of MPs cannot unite around a proposal because Labour's policy black hole prevents there being a majority for any of them.

That makes Corbyn the most important person in British politics. He can whip in favour of one of these options and suddenly, with the assistance of other opposition parties and a dozen or so moderate Tories, there is a majority.

There are now only three options for him to choose from: No-deal, an alternate deal or a People's Vote.

No-deal happens automatically on March 29th, unless something stops it. Corbyn says he will not let that happen. So let's be clear what that entails. It is not a question of refusing to back a motion on no-deal. There is no motion to be delivered on it. It is the default eventuality. He has to back an alternative proposal to prevent it.

Option two is an alternate deal. May says she's interested in working across the aisle. Michel Barnier has said that all sorts of options are available at the EU level if the UK shifts its red line.

Corbyn could right now sign up to customs union and single market membership and try to force it on the prime minister as the price of his cooperation. Even without her, he might be able to find a Commons majority for it. None of this vague meaningless rubbish about a 'close single market relationship', none of the shifty semantic contortions. Single market membership.

Yes, that means accepting state aid rules. They will be a fixture of any Brexit deal whatsoever and anyway they don't stop Corbyn doing anything.

And yes, that means accepting freedom of movement. Good. It is a gift, allowing us to live and work and retire wherever we like. It brings bright young people to this country to help care and pay for our aging population. It makes this a more vibrant, diverse and beautiful place to live. We were told Corbyn would be a brave and principled figure who would stand up to the ignorance of the right-wing mainstream media. So let's see it.

But Corbyn fears this option, because he would suddenly be involved in delivering Brexit. He fears being penalised by the Remainers in his party. He fears being tainted by the consequences of what is happening in the eyes of the general public. He fears he'll no longer be able to blame it all on the government.

The third option is a People's Vote. Everything is primed for this. Europe has made it clear it would extend Article 50 to hold it and that it would offer a window that went beyond the elections in the summer, allowing enough time to do it properly. Morally, the case is watertight. With no mandate for May's deal or anything else, and parliament in deadlock, we need public support for whichever option takes place. If that requires people to get up one day and go vote again, then so be it.

Corbyn's emissaries on earth cast these arguments aside. They hate talking about a second referendum. Even getting them to say the words is like taking a child to the dentist. He's scared that grasping that nettle would cost him his Leave voters.

And it is true. There are dangers for him everywhere. But he has to grasp one of these nettles. He has to adopt a position. Doing nothing does not excuse him of responsibility for what happens next. It makes him as culpable as the government and even more cowardly. It is an active choice and a reprehensible one - the choice of party over country, self interest over national interest. The same choices May made. The choices that make life easier day-to-day but see you condemned by the history books.

The time for constructive ambiguity is over. Corbyn cannot hide any longer. He has to make a decision.